Setting :use-markup and :text is currently not idempotent, and it
depends on the ordering, e.g.:
g_object_set (actor, "use-markup", TRUE, "text", value, NULL);
does not yield the same results as:
g_object_set (actor, "text", value, "use-markup", TRUE, NULL);
This is particularly jarring when using ClutterText from ClutterScript,
but in general GObject properties should not rely on the order when used
from g_object_set().
The fix is to store the contents of the ClutterText as a separate string
from the displayed text, and use the contents, instead of the displayed
text, when toggling the :use-markup property.
Let's also add a unit test for good measure, to try and catch
regressions.
https://bugzilla.gnome.org/show_bug.cgi?id=651940
